This invention is directed to a waterbased coating composition and in particular to a waterbased coating containing a methylol (meth)acrylamide acrylic polymer, an acrylic hydrosol and an alkylated melamine crosslinking agent.
Methylol (meth)acrylamide acrylic polymers are polymers containing polymerized monomers of methylol methacrylamide or methylol acrylamide or any mixtures thereof.
Water based coating compositions useful for base coats and clear coats for automotive applications are shown in Wilfinger et al U.S. Pat. No. 4,730,020, issued Mar. 8, 1988. Waterbased coating compositions containing hydrosols are shown in Cowles et al U.S. Pat. No. 4,797,444 issued Jan. 10, 1989, Aluotto et al U.S. Pat. No. 4,477,609 issued Oct. 16, 1984. The preparation of acrylic hydrosols is shown in Hoefer et al U.S. Pat. No. 4,623,695 issued Nov. 18, 1986. However, none of the compositions shown in the art form finishes having properties that are required in particular for exterior finishes of automobiles and trucks.
To date, solvent based paints have been the predominant finishes used to coat the exterior of automobiles and trucks. These solvent based paints have excellent adhesion to the substrate and provide properties such as weatherability, gloss, hardness, distinctness of image that are required for finishes of the exterior of automobiles and trucks. To meet desired standards of reduced solvent emissions and achieve lower baking temperatures to save energy, waterbased paints were suggested for use. However, none of the known water based paints form finishes that have the necessary properties for automotive and truck use along with lower baking temperatures.